The present invention relates to backpack spraying equipment.
Equipment of the type in question comprises a base, at bottom, a tank containing the spraying liquid and secured to the top of the base, a compression chamber, connected by way of a pipeline to a spray lance, and a pump by which liquid is drawn from the tank and supplied to the compression chamber.
In the most familiar type of embodiment, the pump and compression chamber are coaxial and disposed internally of the tank, the piston of the pump being rigidly associated with the compression chamber and the cylinder rigidly associated with the tank. The pump is operated by a lever pivoted to the base and impinging directly or indirectly on the compression chamber by way of a connecting rod mounted externally of the tank; accordingly, the chamber is reciprocated repeatedly into and from the tank, retracting and extending as its movement is transmitted to the piston of the pump.
In this type of embodiment, the piston connecting rod is somewhat long, and a source of problems in ensuring an efficient seal between the different parts of the pump, not least between the tank and compression chamber. Difficulties with seals are aggravated further by the fact that the spraying liquids carried in the tank will often be abrasive or induce encrustation; accordingly, the materials used in construction must be especially resistant to such liquids. Moreover, it will be appreciated that the connecting rod or the piston rod operates continually under axial compression forces, and that such forces dictate certain minimal structural requirements in their turn. An additional problem encountered is that of the difficulty in servicing the various moving parts of the pump as a result of their being accomodated internally of the tank. Other designs of backpack spray equipment feature a pump that is disposed other than coaxially with the compression chamber and located externally of the tank, though here again the majority of the moving parts operate internally of the tank, immersed in the spraying liquid.
In another type of embodiment, the operating lever carries a pair of short arms articulated with the bottom ends of respective connecting rods, of which the top ends are articulated with the compression chamber operating the piston of the pump; in this design, problems associated with axial compression are overcome by eliminating the relative forces entirely, though one is still left with a similar number of moving parts operating immersed in the spray liquid.
Other designs feature location either of the pump or of the compression chamber externally of the tank and of the base, but with the obvious risk of damage to exposed parts through impact.
An embodiment also exists in which the compression chamber is integral with the tank, and the piston slides in a cylinder associated with the base of the tank.
Yet another type of embodiment features two pumps similar to those outlined above, of which the piston rods run substantially parallel the entire length of the tank and are operated by respective connecting rods disposed substantially parallel to them. Notwithstanding the compression chamber in this embodiment is located internally of the base, connected to the pump on the one hand and to the outlet pipeline supplying the lance on the other, problems deriving from the length of the connecting and piston rods and the axial compression forces to which they are subject remain markedly in evidence as in the former instances described.
One drawback common to all conventional backpack equipment is the absence of some facility whereby the operator can be advised of arrival at maximum permissible pressure internally of the compression chamber. Such a shortcoming is serious in nature, in view of the fact that the operator needs to keep the compression chamber substantially at maximum pressure in order to obtain maximum spray force at the outlet; consequently, the permissible limit is easily exceeded, and with clear risks in terms of damage.
Another drawback common to all designs of equipment thus far described relates to their cost, and more exactly, to the fact that one is denied the freedom to design models of different capacity utilizing the same components, as far as possible. In most of the conventional designs mentioned, in fact, the moving parts utilze the full height of the tank, so that an increase in capacity using the identical moving parts is possible only by increasing the transverse dimensions of the tank, which in turn signifies distancing the center of gravity of the tank from the operator and upsetting the balance of the entire pack.
Accordingly, the object of the present invention is to provide backpack spraying equipment affording economy in design, practical, simple and safe in use and easy to service.